Reese Witherspoon marked her last day of the summer holidays by posting an envy-inducing picture of herself on Instagram.MORE: Reese Witherspoon shares rare family photos with lookalike mom Betty to mark special celebrationThe actress shared a stunning photo showing her in a wrap dress by her brand Draper James, flat sandals, and sunglasses as she sipped a cocktail whilst sat in a sofa chair just by the ocean. WATCH: Reese Witherspoon's throwback marks big milestoneThe 45-year-old has been